Durability of basalt FRP reinforcing bars in alkaline solution and moist concrete environments

The durability performance of basalt fiber-reinforced polymer (BFRP) reinforcing bars conditioned for 3, 6, and 9 months at temperatures of 20, 40, and 60 °C was investigated. BFRP specimens were exposed to two environments: moist concrete and an alkaline solution simulating the concrete pore solution. Correlations among tensile strength, moisture uptake, matrix digestion, and microstructure characteristics were furnished. The degree of deterioration was more sensitive to the conditioning temperature than the conditioning duration. The tensile strength retentions of the specimens conditioned in the alkaline solution at a temperature not exceeding 40 °C were comparable to those conditioned in the moist concrete environment irrespective of the conditioning duration. Conditioning in the alkaline solution at 60 °C for a duration ≥6 months had a more detrimental effect on the microstructure and strength of the BFRP than encasing in moist concrete. After 9 months of exposure at 60 °C, the specimens conditioned in the alkaline solution lost 29% of the initial tensile strength while those encased in moist concrete lost only 15%. The intensified tensile strength reduction caused by the former conditioning scheme was due to disintegration of the matrix and degraded fiber-matrix interfacial bond caused by a higher moisture uptake and development of more hydroxyl groups during conditioning. The accelerated aging test results were utilized to develop a master curve for service life prediction of BFRP bars.